The present invention relates to a polymer-electrolyte lithium secondary battery (lithium polymer secondary battery). Furthermore the invention relates a lithium polymer secondary battery containing a polymer electrolyte polymerized in the battery.
Development of a miniature, light and repeatedly chargeable secondary battery having high energy density has lately been desired with development of electronic equipment. A lithium secondary battery has gained attention because it is safe, and has high energy density per volume or per weight and a long life time. As a lithium ion secondary battery, one containing liquid electrolyte has been practiced. However, a lithium polymer secondary battery having a gel polymer electrolyte is gaining attention as a future lithium secondary battery.
It has been known that a lithium polymer secondary battery is prepared by insertion of a polymer sheet between a positive and negative electrodes and gelling of the polymer.
However, electrodes and polymer electrolyte in a conventional lithium polymer secondary battery do not adhere well because of the manufacturing processes of the polymer electrolyte and the structure of the battery. There are also problems that the battery has high battery structural pressure (pressure inside of the battery), varied temperature distribution in the battery during charge and discharge, and bad heat radiation. Therefore, the active materials of the battery easily deteriorate and the battery does not have good cycle characteristics.
A lithium polymer secondary battery having a polymer electrolyte that is obtained by polymerization in a battery is also known. However, it is difficult for a monomer for the polymer electrolyte to penetrate into a fine porous film located between a positive and negative electrode stuctrure that is formed by insertion of a fine porous film between positive and negative electrodes which are wound into a spiral and then pressed to a flat plate. There is also difficulty in providing good adherence between the polymer electrolyte and electrodes.
An object of the present invention is to provide a lithium polymer secondary battery which has a suitable structure to use a polymer electrolyte polymerized in a battery and has good cycle characteristics.
The present invention provides a lithium polymer secondary battery having at least a basic battery cell including positive and electrodes and a polymer electrolyte in an outer can, wherein one of the electrodes is U-shaped and the other electrode is inserted in the U-shaped electrode and the polymer electrolyte includes a polymer containing polyalkylene oxide and a solvent and is polymerized in the battery. The thickness of the battery is not greater than 2 mm.
FIG. 1 is a cross section of the structure of a basic battery cell of the present invention.
FIG. 2 is a cross section of an embodiment of a lithium polymer secondary battery of the present invention.
FIG. 3 is a perspective view of the exterior of an embodiment of a lithium polymer secondary battery of the present invention.
FIG. 4 is a perspective view to explain the electrode overlapping area of the present invention.
FIG. 5 is a plan view to explain the electrode overlapping area of the present invention.